Reactive electron discharge circuits



Nov. 28, 1.944.

J. F. wlLcox ET AL 2,363,918

Y REACTIVE ELECTRON DISCHARGE CIRCUIT s `Filed. July l1, 1942 CARR/en AWA v5 AMPLIFIER l(Has/c.) Y

.(3.87 mrs? 'Patented Nov. 228, 1944 UNITED 'STATES PATEN 'r ori-lcsREACTIVE ELECTRON DISCHARGE CIRC'UI James F. Wilcox, Scotiawand Edwin W.Kenefake,

Schenectady,

N. Y., 'assignorsto General Electric Company, a corporation of New YorkApplication July 11, 1942, Serial No. 450,498

7 Claims.

devices are commonly connected across a tuned circuit to adjust,according tothe potential on the control electrode, the resonantfrequency of the tuned circuit.

Such resonant circuits, whose operating frequency may be readilyadjusted, are used to produce frequency modulated carrier waves, theadjustably tuned circuit being the frequency controlling ciruit of anoscillator. It has been found that one of the advantages offrequencymodulation is attained when th'e amount of frequency shift ofthe carrier wave is greater than the highest frequency of the modulatingsignal. For

` phone Ill modulate the resonant-frequency of a example, an ordinaryaudio signal may contain components up to about 5000 cycles making itdesirable to shift the frequency ofthe carrier wave about 25,000 cyclesfrom its mean frequency in either direction. l

Adjustably tuned circuits, as described above,

are capable of varying their resonant frequency an amount in the orderof 5 or 6% of the carrier frequency, asthey are usually constructed. Itis therefore evident that, if the carrier frequency is (c1. 11s-11m) Itis a 4corollary object of our invention to provide such a reactancedevice which is especially useful at low carrier wave frequencies forproducing a larger frequency swing for the purpose of producingfrequency modulations.

The features of our-invention which we believe to be novel are set forthwith particularity in the appended claims. Our invention itself, both asto its organization and manner of operation, together with furtherobjects and advantages. thereof may best be understood by reference tothe j following description taken in connection with the accompanyingdrawing in which Fig. lillustrates one embodimentof our. invention andFig. 2 shows certain Acharacteristics of the appa- I ratus of Fig. l.

In the apparatus of Fig. 1 signals from a microcircuit including adischarge device ll, the resonant circuit being maintained inoscillation by a discharge device I2, and such frequency modulatedoscillations being amplified through a power amplifier *I3 and.impressed on a power line I4 through a coupling condenser l5. Thecathode I6 of the oscillating discharge device l2 is grounded, thecontrol electrode Il thereof is connected through a grid leak resistance|73 to ground' and is coupled through a coupling condenser i9 to oneterminal 28 of a tuned circuit comprising that part of an inductance 20between an intermediate. tap 22 and terminal 20, and a variable:condenser 2l connected between tap 22 and termivnal 2s. Theintermediate cap 221s connected to less than about twenty times thehighest frequency component of the signal to be transmitted, the usualtype of adjustable frequency tuned circuit is not capable of shiftingthe frequency of the carrier wave sumciently to give the large frequencyswing desired. For example, with a carrier wave of 50 kilocycles, asfrequently used for carrier current transmission, a 3% swing in eitherdirection would be about 1500 cycles in either di rection. If thehighest frequency component of' the signal to be transmitted were only3,000 cycles, with such a low ratio of the highest signal frequencytothe `carrier frequency swing, a low I signal to noise vratio results.

It is an object of our invention to provide a new and improvedadjustable reactance discharge device whose reactance is vvariablelinearly with respect toa control voltage over a wider range than hasheretofore been attained.

the anode 23 .of the device l2, and is coupled through a suitablecoupling condenser 24 to the amplifier I3.

Discharge current for the device l2 is supplied from the positiveterminal of a source 25 of operating potential, whose negative terminaly is grounded through an intermediate tap 26 of the inductance 20between the tap 22 and'terminal 28 of the inductance. The tap 26.isbypassed to ground by a bypassing condenser 2l for high frequencycurrents.

So connected, with thetap 26 and the cathode i6 of device l2 at fixedpotentials, and opposite terminals 22 and 28 of the tuned circuitincluding inductance 20 and condenser 2| coupled respectively to theanode 23 and control ,electrode l1 of the device. l2, continuousoscillations are maintained in thetuned circuit, at a frequencydetermined by the resonant frequency of the tuned circuit.

The discharge device ll,` which controls the resonant frequency of thetunedcircuit including the inductance 20 and condenser` 2 I, has ananode 38 connected to that terminal of the inductance 20 opposite theterminal 28. The cathode 3| -of device II is connected to ground througha biasi ing resistance 32 in parallel with the bypassing condenser 33.The rst, or control, electrode 34 is connected to ground through a pairof resistances 35 and 36, connected in series, and through themicrophone I0. The second or screen electrode 31 of the device I I isconnected to cathode 3| through a suitable bypassing condenser 38, andis also connected through a resistance 39 to the positive terminal ofthe source 25.

The control electrode 34 ofthe device I I is excited with a voltagewhich is out of phase with the voltage across the tuned circuit 20, 2|,by a ing current through the resistance 35 produces a leading voltagethereacross, which in turn appears on the control electrode 34 of deviceII and causes a leading current to flow in the discharge path of thedevice I I.

By reason of lthe fact that the phase shifting network 35-40 isconnected across the entire. tuned circuit including condenser 2| and apori tion of inductance 2li, and the fact that an intermediate tap 28 ofthat tuned circuit is maintained at a fixed potential, the alternatingpotential impressed on the control electrode 34 of the device II withrespect to cathode 3| may be made to differ in phase by exactly 90 fromthe alternating potential across condenser 2|. That is, by suitablyproportioning the condenser and resistance 35, the voltage between thecontrol electrode 34 of device II and intermediate tap 26 of inductance20 may be made to be exactly' 90 out of phase with the alternatingpotential between tap 22 and terminal 28 of inductance 20. The properadjustment is attained when the voltage across resistance 3 5 has a.component in phase with the voltage between taps 22 and 28 ofinductance 20 equal to the alternating potential'between taps 26 and 28of inductance 20.

By reason of the autotransformer action of the inductance 2|), a largerhigh frequency potential appears on the anode 80 of the reactance deviceII than on'the anode 23 of the oscillating discharge device I2. "Iihishigher alternating potential on the anode 30 of the device II produces alarge reactive current flow through the impedance presented by thedischarge path of the. device II, so that the magnitude of the reactancepresented by device II to the anode circuit of device I2 is smaller thanif the anode 30 were connected directly lto* tap 22 and anode 23 ofdevice I2. Therefore, device in shunt to the microphone I0, so that, inconnection with the resistance 36, a low pass filter iS formed toprevent the appearance across the "microphone I0 of alternatingpotential of the frequency of the carrier wave generated by device I2.

The reactance of condenser 42 should besubstantial at the frequency ofsignals from microphone I0 to avoid undesirable attenuation thereof. i

In Fig. 2 a curve 50 illustrates the relation between the instantaneoussignal potential from microphone I0 and the resulting frequencydeviation of the carrier wave generated by the device I2. In this figurethe instantaneous signal potentials in volts are plotted as abscissae,and the resulting frequency deviations in kilocycles as ordinates. aszero, the carrier frequency was actually 88.5 kilocycles and the`instantaneous signal potential 3.87 volts. By a change of about 2 voltson either side of this operating condition, th'e frequency of thecarrier wave was changed linearly about 5 kilocycles in eitherdirection. The total linear frequency change thus produced was more than11 percent of the'average carrier frequency.

When an autotransformer arrangement, such as that in Fig. 1 includingthe inductance 28, is utilized to produce a wide linear frequency swingin response to a modulating potential, it is desirable that amplitudemodulation of the frequency modulated carrier wave be minimized. If analternating potential be applied to the control electrode 34 of deviceII which has a component in phase with the alternating potential betweentaps 22 and 28 of the inductance'20, a regenerative or degenerativeeffect is produced upon the tuned oscillator circuit through the actionof current flowing through the anode 30 controlled in accordance withthe alternating potential on the control electrode 34. This regenerativeor degenerative action results in the production of amplitudemodulations of the oscillating potential maintained in the tuned circuit20, 2| by the oscillating discharge device I2.

In order to minimize said amplitude modulation.in the presence of thewide frequency swing attainable with our `frequency modulationarrangement, it is desirable to use the phase shiftlist ing networkincluding condensers 40 and 4| and resistance 35, which is effective toimpress an alternating potential on the control electrode 34 I withrespect to cathode 3| of device which is exactly 90 out of phase withthe alternating potential across the tuned circuit including condenser2| and that portion of inductance 20 between the taps 22 and 28. l

Our invention may be utilized to modulate the frequency of any carrierwave, such as for a radio transmitter, over a very wide frequency band.It may, in fact, be utilized to take a large reactive current from anysource of alternating potential, where such a reactive current isdesired.

While we have shown and described .a particuf lar embodiment of ourinvention, it willbe ob- II appears as. a larger capacity at the anodeof 'device'V I2 than-if the two anodes 23 and 30 were connecteddirectly. :The micro.- phone Il! is so connected as tovary the averagepotential on the control electrode 34 at signal frequency, therebyadjusting in accordance with the signal the amount of reactive currentilowing .through the discharge D th of device j I.

vious to those skilled in the art that changes and modifications may bemade without departing from our invention in its broader aspects, and

aim in the appended claims to cover all such changes and modificationsas fall withinwe, therefore,

the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination, an oscillator including an lllectron discharge devicehaving an anode and a A suitable bypassing condenserl 42A is connected'u control electrode connected to opposite terminals At the frequencydeviation indicated `of a resonant circuit to excite oscillationstherein, said resonant circuit including a winding, a second electrondischarge device having an anode, a cathode and a control electrode, asecond winding connected in series with said winding and comprisingtherewith an autotransformer, said autotransformer having its endterminals connected between the anode and cathode of said seconddischarge device. means for supplying .to the control electrode of saidsecond discharge device oscillations having such phase relations tooscillations on the anode of said second discharge device that areactive current flows between the anode and cathode thereof and throughsaid autotransformer, and means for supplying a variable'unidirectionalpotential to the control electrode of said second electron dischargedevice to vary said reactive current and thereby to control the tuningofsaid resonant circuit and the frequency of oscillations excitedtherein by said iirst discharge device, said autotransformer increasingthe reactive effect of` said second electron discharge device upon saidresonant, circuit and extending the range of said frequency variations.

y 2. In combination, a source of alternating po` tential, means fortaking'from said source an adjustable reactive current, said meanscomprising an electron discharge device having an anode, a cathode, anda control electrode so connected across said source that a reactivecurrent ows between said anode and cathode and the impedance of saiddevice between said anode and cathode simulates a reactance, meanscomprising a step-up autotransformer interposed between said source andsaid device, said autotransformer having its end terminals connectedbetween said anode and cathode and an intermediate portion thereofconnected across said source thereby to increase the reactive e'ect ofsaid device on said source, and means to modulate the current betweensaid anode and cathode in accordance with a varying electromotive forcethereby to modulate the reactive current drawn -by said device from saidsource in accordance with the variation's of said electromotive force.

3. yIn combination, a source of alternating potential, a reactancedevice comprising an inductance and arranged to take a reactive currentfrom said'source, means for impressing potential from said source acrossa portion of said inductance, an electron discharge device having -ananode, a cathode and a control electrode, said anode and cathode beingconnected to electrically spaced points of said inductance includingVappreciably more of said inductance than said portion thereof, and phaseshifting means for impressing alternating potentials from said sourcebetween said control electrode and said cathode in displaced time-phaserelation with respect to the alternating potential between said anodeand cathode. v

4. In combination, a source of alternating potential, a reactance'devicecomprising, an inductance and arranged to take a reactive current fromsaid source, means for impressing potential from said source across aportion of said induct.. ance, an electron discharge device having ananode, a cathode and a control electrode, saidV anode and cathode beingconnected across a second portion of said inductance greater than andincluding said rst portion, and means comprising a reactance and aresistance connected serially across said rst portion of said inductancefor impressing between said control electrode and said cathode analternating potential derived from said source of potential anddisplaced in time-phase relation withA respect thereto, said meanscomprising a connection between said control electrode and a pointbetween said reactance and resistance.

5. In combination, an oscillator including an electron discharge devicehaving an anode and a control electrode connected to opposite terminalsof a resonant circuit to excite oscillations therein, said resonantcircuit including a winding, a second electron discharge device havingan anode, a cathode and a control electrode, a second winding connectedin series with said winding and comprising therewith an autotransformer,said autotransformer having its end terminals connected between theanode and cathode of said second discharge device, and phase shiftingmeans connected to derive from said resonant circuit and apply to thecontrol electrode of said second electron discharge device analternating voltage in substantially quadrature relation with respect tothe voltage of said resonant circuit thereby to effect the iiow of `areactive current through said second electron discharge device and saidautotransformer and to minimize any tendency of said connected in serieswith said iirst inductance, an

electron discharge device having an anode, a cathode and controlelectrode, means for impressing alternating potential from said tunedcircuit between said control electrode and cathode in displacedtime-phase relation with respect to the .phase of the alternatingpotential of said source, means for connecting said anode and cathode tothe electrically remote terminals of said inductance, whereby theauto-transformer action oi' said inductance increases the reactiveeiifect of said discharge device and a component of said alternatingpotential between said control electrode and cathode in phase with thealternating potential of said tuned circuit tends to produce amplitudemodulation of said alternating potential onsaid tuned circuit, and meansfor increasing the time phase relation of alternating potential betweensaid control electrode and cathode with-respect to the timev phase ofthe alternating potential across said tuned circuit'sub-A stantially toa quarter wave of said alternating potential to minimize such amplitudemodulation.

7. A variable frequency oscillation generator comprising an inductance,a condenser connected across a portion of said inductance and forming'with said portion a tuned circuit. means for maintaining anelectrically intermediate point of said portion of said inductance. at axed potential, means for maintaining oscillations in said tuned circuit.an electron discharge device having an anode, a cathode and a controlelectrode, said anoder being connected to a rst terminalof saidinductance electrically spaced from said tuned portion and said cathodebeing maintained at a second fixed potential and connected to a secondterminal of said inductance and means for impressing an alternatingpotential between said control electrode and cathode in displacedlcomprising a resistance and reactance serially connected in shunt tosaid tuned circuit, said control electrode being connected between saidrelactance and resistance, said reactance at the resonant frequency ofsaid tuned circuit being so related to said 'resistance that thealternating potential impressed thereby between said control 5 isminimized.

JAMES F. Wmcox.

Enwm w.

